Install a session border controller – An SBC is a specialized device used to facilitate the communication of VoIP conversations over the edge of a network. Often incorporated into a security device such as a firewall, the SBC goes one step further in ensuring a smooth VoIP deployment while maintaining the utmost level of security. Even though it serves many more purposes such as NAT traversal, QoS, and interoperability mediation, to name a few, security is one of its major functions.